1. Field of the Invention
The present invention relates to a stepping motor used for a device driving source or the like, and a drive device as a stepping motor.
2. Related Background Art
Japanese Patent Application Laid-Open No. 2003-9497 discloses a subminiature stepping motor for aligning phases of stators with each other on a bobbin terminal base. FIG. 14 is an exploded perspective view of the proposed stepping motor.
In FIG. 14, reference numeral 111 denotes a magnet multipolar-magnetized in a circumferential direction, and 112 a shaft, which constitute a rotor 110. Two sets of stators of similar configurations are provided as stators 120 opposed to the rotor 110, and arranged in both ends of the magnet 111 in an axial direction so as to face each other. The stator 120 includes an inner yoke 121, a coil bobbin 122, an outer yoke 123, and a cylindrical member 124 for magnetically and mechanically connecting inner-diameter sides of the inner and outer yokes 121 and 123. The coil bobbin 122 is made of an insulator such as a resin, and a bobbin terminal base 122a is located on its outer peripheral side. The inner and outer yokes 121 and 123 are both made of magnetic materials, and tooth-shaped magnetic pole portions 121b and 123b thereof face an outer peripheral surface of the magnet 111. The magnetic pole portion 123b of the outer yoke 123 is arranged in a position having a phase difference of an electrical angle of 180° with respect to the magnetic pole portion 121b of the inner yoke 121. It is the bobbin terminal base 122a of the coil bobbin 122 that regulates relative positions of the magnetic pole portions 123b and 121b. This construction will be described by referring to FIGS. 15A and 15B.
FIG. 15A is a view of the coil bobbin 122 seen from an axial direction, and FIG. 15B a sectional view of the coil bobbin 122. Stator regulation portions 122d and 122e are disposed in the bobbin terminal base 122a of the coil bobbin 122. The stator regulation portion 122d is engaged with the magnetic pole portion 121b of the inner yoke 121, and the stator regulation portion 122e is engaged with the magnetic pole portion 123b of the outer yoke 123. By these engagements, the inner and outer yokes 121 and 123 are positioned with respect to the coil bobbin 122, and the inner and outer yokes 121 and 123 are correctly held in positions of electrical angles of 180° to each other.
In the stepping motor of the aforementioned construction, a rotational direction position between the two sets of stators 120 must be set in a position of a predetermined angle (usually an electrical angle of 90°). Accordingly, an opening 131a of a motor case 131 is engaged with a yoke regulation portion 122f disposed in the bobbin terminal base 122a, and a position of the yoke regulation portion 122f is set so as to form predetermined shifting angles with respect to the stator regulation portions 122d and 122e, whereby a phase difference is created between the two stators 120. Thus, positioning is facilitated, achieving enhanced ease of assembly.
As another conventional example, Japanese Patent Application Laid-Open No. 2003-70224 discloses a stepping motor in which two sets of stators is positioned by different components. FIG. 16 is an exploded perspective view of the stepping motor.
In FIG. 16, reference numeral 303 denotes a first magnetic unit which includes a stator (inner and outer magnetic pole portions) facing a magnet, and a coil for exciting the stator, these components being covered with resin to be integrated together. Similarly, reference numeral 304 denotes a second magnetic unit which includes a stator (inner and outer magnetic pole portions) facing the magnet, and a coil for exciting the stator, these components being covered with a resin to be integrated together. Reference numeral 301 denotes a magnet, 302 a shaft having the magnet 301 fixed thereto for rotatably holding the magnet 301, and 305 and 306 bearings.
In the stepping motor of the aforementioned construction, the magnet 301 is held between the two magnetic units, namely the first and second magnetic units 303 and 304, from both ends. Specifically, this stepping motor is constructed as a cylindrical motor by butting the first and second magnetic units 303 and 304 each covered with a resin against each other to be integrated together. A portion having a shape of a pin, a projection, or the like, is disposed in the butted portion to enable positioning, with their respective outer magnetic pole portions maintaining predetermined angles, and then an adhesive resin is applied on the butted portion, and hardened and fixed.
Meanwhile, in many cases, compact cylindrical stepping motors are structured in such a manner that, to facilitate power feeding to the coil for exciting the stator, a terminal base equipped with a terminal pin is disposed in the bobbin around which coil wire is wound, a terminal of the coil wire is wound on the terminal pin, and a flexible printed circuit (hereinafter abbreviated as FPC) or the like is electrically connected to the terminal base.
In subminiature stepping motors having a small outer diameter, the terminal base is also formed small. Accordingly, measures are taken to overcome problems caused by loads applied to the terminal base and the FPC when the FPC or the like is connected to the terminal base. In other words, many proposals have been made about contrivances for preventing the FPC falling-off from the terminal base or the terminal base from being damaged, and contrivances utilizing the protruding configuration of the terminal base from the motor outer peripheral surface.
In FIG. 16, in the first and second magnetic units 303 and 304, terminal bases 307 and 308 are integrally formed with bobbins (not shown), respectively. The terminal bases 307 and 308 are arranged with flanges of the bobbins extending and protruding from the motor outer peripheral surface, and respectively support terminals 307a and 308a for winding lead wires of the coils wound on the bobbins. Members 309 and 310 made of resins are additionally disposed in the terminal bases 307 and 308, respectively.
The first and second magnetic units 303 and 304 are disposed so that their longitudinal (axial) ends face each other, and the resin members 309 and 310 are disposed between the terminal bases 307 and 308, whereby the terminal bases 307 and 308 are increased in strength. Accordingly, it is possible to prevent the terminal bases 307 and 308 from being destructed due to an external force applied thereto when the FPC or the lead wire of the coil is connected to the terminal bases 307 and 308.
There has been proposed a technique for preventing an FPC from being disconnected due to an external force (e.g., Japanese Patent Application Laid-Open No. H6-237551).
FIG. 17 is a sectional view showing a construction of a spindle motor disclosed in Japanese Patent Application Laid-Open No. H6-237551.
In FIG. 17, the spindle motor is a motor used for rotationally driving a floppy (registered trademark) disk or the like, and includes a spindle 401, a rotor 402, a coil 403, a stator portion 404, a base 405, a sleeve 406, an FPC 407, and a reinforcing member 408.
The FPC 407 on which a power supply circuit or the like for feeding power to the coil 403 is mounted includes a through-hole 407a, and the sleeve 406 disposed in the stator portion 404 is inserted into the through-hole 40-7a. The reinforcing member 408 is disposed below a fixing portion 407b of the FPC 407, and the reinforcing member 408 is pressed and fixed onto the sleeve 406. The above structure, in which the FPC 407 is fixed to the stator portion 404 through the reinforcing member 408, enables fixing of the FPC 407 with sufficient strength. Accordingly, even when an external force is applied to the FPC 407, there is no fear of the FPC 407 being damaged or the fixed portion being destroyed.
However, in the stepping motor shown in FIG. 14, the alignment of the inner and outer yokes 121 and 123 is carried out directly by the bobbin terminal base 122a, and thus assembly can be very accurate. However, the phase alignment between the two sets of stators 120 is carried out in such a manner that phases of the stators 120 are aligned with each other through the two stages of alignment between the coil bobbin 122 and the stator 120 and alignment between the coil bobbin 122 and the motor case 131, and the dimensional accuracy of phase alignment between the stators 120 is not really high in consideration of component tolerances and the like. Thus, the use of another member (corresponding to the motor case 131) provided with the regulation portion for aligning the phases of the stators with each other by one component causes problems of an increase in the number of components, complex component construction, and the like.
In the stepping motor shown in FIG. 16, the positioning is not so accurate because it is carried out by the resin which covers the exterior of the stepping motor. However, as compared with the stepping motor shown in FIG. 14, the accuracy is higher because the motor case is not interposed. Moreover, since the motor case component itself is not necessary, the stepping motor has an advantage that the number of components can be reduced and assembly is easy. However, there is a disadvantage of increased costs because insert molding for covering the stator or the coil with the resin is necessary.
The stepping motor shown in FIG. 16 employs the structure of filling the portion between the terminal bases, to which the FPC or the like is connected, with the resin, thereby contributing to the reinforcement of the terminal bases themselves. However, there is a fear of falling-off of the FPC from the terminal base when an external force is applied to the FPC or the like. Besides, because of the largely protruding configuration of the terminal base itself from the motor outer peripheral portion, miniaturization is impossible.
Furthermore, the motor shown in FIG. 17 employs the structure in which the sleeve is inserted into the through-hole of the FPC and the reinforcement is provided by the reinforcing member, whereby destruction is not liable to occur even when an external force is applied to the FPC. However, when the structure of FIG. 17 is applied to a two-phase compact cylindrical motor similar to the stepping motor shown in FIG. 16, the two coils are arranged in separate positions on the same axis in FIG. 16, and thus arrangement similar to the structure of FIG. 17 is structurally difficult.